ITT Corinth has made 554 and 2554 single line wall phones for decades.
They're now called Corteclo. I would imagine that's what they're talking about?
At a minimum, I'd never mount the phone next to a jack. Leave the wall jack off, and put a surface mount jack inside the wall. I would personally just crimp on a mod plug to the cable, bring it through a small hole, and plug it into the back of the phone before I hung it on the screws. You may have to crimp it twice to get the polarity correct (then write down the way to crimp it on the cover of your manual for that system).
That's been the standard method for mounting many wall phones since the Merlin days. Some wall phone kits gave you space to mount the surface mount jack in the wall base.
If you have a single gang box in the wall, just leave the surface mount jack inside the box and use a cord to connect to the phone when you hang the screws.
You may find that the screw spacing is the same as that on a single gang outlet box if you hold a regular flush jack to the back of the phone?
If it's some kind of Chinese phone, they don't really follow standards until someone complains (they copy, but not necessarily exactly). They've never really used phones in China (not much copper plant there), so the guy who designed it probably had no idea.
It's expensive to change a mold, and if they already have phones out there it makes them incompatible with what's out there, if they change it now.
Have fun... Mike
